Whether you had a land enter the battlefield under your control this turn is checked as this spell resolves, not as you cast it.

3/1/2010

Having more than one land enter the battlefield under your control this turn provides no additional benefit.

3/1/2010

The landfall ability checks for an action that has happened in the past. It doesn’t matter if a land that entered the battlefield under your control previously in the turn is still on the battlefield, is still under your control, or is still a land.

3/1/2010

Once the spell resolves, having a land enter the battlefield under your control provides no further benefit.

3/1/2010

The effect of this spell’s landfall ability replaces its normal effect. If you had a land enter the battlefield under your control this turn, only the landfall-based effect happens.

3/1/2010

You must choose two targets as you cast Searing Blaze: a player and a creature that player controls. If you can’t (because there are no creatures on the battlefield, perhaps), then you can’t cast the spell.

3/1/2010

If either target is illegal by the time Searing Blaze resolves, it still deals damage to the other target.